What is the equation of the line that passes through the points (3, 6) and (8,4)

In the equation y=mx+b, 'm' is the slope of the line and 'b' is the y-intercept.  
First, you should find the slope of the line.  To do this, use the equation M=y2-y1/x2-x1.  Using the two given points (3,6) and (8,4), you can solve for M.  
M=4-6/8-3
M=-2/5 (-0.4 in decimal form)
Now, your equation is y=-0.4x+b
Next you must solve for b to find the y-intercept.  You can do this by subbing one of the given points in for x and y.  
Using the point (3,6):
y=-0.4x+b
6=-0.4(3)+b
6=-1.2+b
Isolate b:
6+1.2=b
b=7.2
And now you have the equation of the line!
y=-0.4x+7.2 (IN FRACTION FORM: y=-2/5x+36/5)